Inhalers are commonly used for delivery of a wide range of medicaments. The inhaler holds a cannister of medicament which is actuated by compression to deliver a dose of medicament through a mouthpiece. The inhaler may be provided with an actuation mechanism for compressing the canister. This may be a breath-actuated mechanism which is arranged to actuate the canister in response to inhalation at the mouthpiece. Typically, a breath-actuated inhaler includes a pre-loading mechanism for loading a resilient loading element with an actuation force for compression of the canister and a triggering mechanism arranged to hold the resilient loading element against compression of the canister and to release the resilient loading element on inhalation.
Known canisters comprise a body having a protruding valve stem and an internal metering chamber which receives a dose of medicament stored in the body. Compression of the valve stem into the body causes the medicament in the metering chamber to be delivered out of the valve stem as a dose. The valve stem is biassed outwardly to re-set the canister after compression to deliver the next dose of medicament. However, if the compression of the canister is released to allow re-set of the valve stem too early, then a full dose is not properly delivered. The present invention is intended to ensure proper delivery of a full dose.